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7.5 Clustering in private networks

In many situations, peers run in hosts of a private networks (see the “Before” part ofFigure4). However, if two or more users that are in the same private network want to playdiﬀerent players, a simple and eﬃcient solution consist in creating a private team using thepeer that belong to the public team as a source fo the private splitter (see the “After” part ofFigure4).∗∗The reader could think that running another peer inside of the private network the same eﬀectcould be achieved. Nonetheless, this is not true because peers know each other by means of a publicNAT end-point and most NATs does not allow to communicate private processes using their publicend-points.Note that, as IP multicasting is available on the private network, the private team shouldbe conﬁgured to take advantage of this fact.

Figure 4: A private clustering scenario. In order
to accomodate several private peers, a private team
T2
can be created using the stream produced by
the private peer that belongs to the public team
T1.

Similarly as it happens with transparent Web proxies, this locality-awareclustering concept could be also used by ISPs in order to minimize inter-ISPtraﬃc. In a nutshell, if a ISP detecs that there is P2PSP traﬃc between “local”peers and “foreign” peers, the ISP could deploy a private team. This can beconﬁgured by ﬁltering the list of peers that the splitter sends to the peers. Thisﬁltering should be performed depending on the locality of the IP addresses of thepeers.